Day 5 and thinking I need to break the fast due to severe weakness

I'm on day 5 of my first ever fast and unfortunately am thinking I need to break it. I've been dealing with an undiagnosed chronic condition with a laundry list of symptoms for over 6 years which is my motivation for fasting. One of these symptoms is systemic fatigue and muscle weakness and when it gets really bad I have difficulty breathing and swallowing, and I'm pretty unsteady on my feet.

I wasn't having these issues very prominently until last night, and I woke up this morning feeling about as weak as I ever do with the associated breathing, swallowing, etc issues. I can only stand up for short bursts as my pulse skyrockets and I feel light headed and somewhat unsteady on my feet.

Is there any chance the weakness will subside or am I best off breaking this fast and trying again down the line?

Any suggestions on what I could do to build up more strength and better prepare for my next fast?

I know I must be quite ill / toxic as this fast has been truly hellish. For the first 3 days I felt like I had a terrible flu, a migraine level headache, really sore eyes, and nausea. At 4am of day 4 I threw up green goo with black flakes in it. My pulse has hovered between 90 and 110, which I've read is indicative of a high toxic load being released to the bloodstream. So I'm disappointed I can't continue as I clearly have a lot of issues that fasting can address, but hope to do better next time after more preparation.